Synthesis of carbon‐14–labelled peptides

Abstract

Carbon‐14 (14C)–labelled active pharmaceutical ingredients (APIs) and investigational medicinal products (IMPs) are required for phase 0/I to phase III mass balance and micro‐dosing clinical trials. In some cases, this may involve the synthesis of 14C‐labelled peptides, and the analysis can be performed by accelerated mass spectrometry (AMS). The 14C‐peptide is typically prepared by the solid‐phase peptide synthesis (SPPS) approach using custom‐made glassware for the key coupling steps. Further modification of the purified 14C‐peptide can then be performed.

Metabolism and Excretion of Therapeutic Peptides: Current Industry Practices, Perspectives, and Recommendations

“…Although 14 C is a commonly used radioisotope, it has limitations compared to 3 H labeling. For example, the specific activity of 14 C is ~450 times lower than that for 3 H (0.0624 Ci/mmol and 28.6 Ci/mmol, respectively) (Dell'isola et al, 2019) which can make detection of the label difficult for low dosed drugs. The specific activity could be increased by introducing multiple 14 C atoms to the same molecule.…”

“…In some instances, peptides are also labeled with 125 I, a common labeling radioisotope for therapeutic proteins or for receptor binding studies. 14 C labeling has advantages compared to other radioisotopes (Dell'isola et al, 2019) especially in comparison to using 3 H which can be lost from the molecule due to hydrogen-tritium exchange (Knadler et al, 1992), and may impact the quantitative analysis in an ADME study. The 125 I labeling technique modifies the structure and composition of the molecule, which may change the ADME property of the peptide particularly for the small ones.…”

Enantioselective Carbon Isotope Exchange

“…Since α-amino acids are one of the key building blocks of life and are found embedded in many approved small molecule drugs and biologics (26,27), there is a strong need for C-labeled α-amino acid targets. 14 C-labeled α-amino acids are now heavily relied upon in drug development, mainly for (pre)absorption, distribution, metabolism, and excretion (ADME) studies (28,29). We recently disclosed a racemic CIE method wherein α-amino acids are directly labeled from their native precursors by undergoing aldehyde-catalyzed carboxylation/decarboxylation in the presence of *CO2 (Fig.…”

Radiolabelling small and biomolecules for tracking and monitoring

“…In the case of 14 C labelling, 14 C containing amino acids are incorporated into the sequence via peptide synthesis. 52 Due to the low molar activity of 14 C isotopes, this is a limitation for some studies, especially in imaging. Higher specic activities can be achieved by radioiodination.…”